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UN investigation found that Syrian Air Force and ISIS have used chemical weapons

This story contains graphic images, including some of child victims.

(CNN)More than 80 people were suffering severe breathing difficulties in Syria's embattled city of Aleppo after another chemical attack Tuesday on a rebel-held neighborhood, said the Syrian Civil Defense, a volunteer rescue group.

The UK-based Syrian Observatory for Human Rights also reported the attack, saying that medical sources accused regime warplanes of pounding the Sukkari neighborhood with barrel bombs "laden with poison gas."

This still from a video shows a girl treated at a makeshift hospital after what a rescue group called a chemical attack on her Aleppo neighborhood.

Harrowing footage distributed by the Syrian Civil Defense -- also known as the White Helmets -- shows small children and other victims being rushed to the makeshift Basel Aslan hospital in the arms of rescuers, gasping desperately for air as they are given oxygen masks.

A young victim breathes through an oxygen mask at a makeshift hospital.

The video also shows a boy being washed with a hose by rescuers after being pulled from the rubble as the sirens of ambulances wail around him.

Another video by the Aleppo Media Center shows a man laying almost lifeless at the same hospital as medics try to pump oxygen into his lungs.

Such scenes are becoming all too familiar in Aleppo, part of which has been held by rebels since July 2015. Government forces in July encircled the rebel-held part of the city in a siege that cut residents off from basic supplies of food, water, fuel and medicine, spawning a humanitarian crisis.

Rebel-held Aleppo has been pounded by the forces of President Bashar al-Assad's regime, backed by Russian air power. Several cases of chlorine gas bomb attacks also have been reported there.

Photos:Aleppo photographer watches city die

Two children walk past a "White Helmet" soon after an airstrike hits the Shaar neighborhood of Aleppo.

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Photos:Aleppo photographer watches city die

Members of the "White Helmets" civil defense volunteers carry the body of a man killed in a Russian airstrike in Andan town in the countryside north of of Aleppo.

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Photos:Aleppo photographer watches city die

Buses piled one on top of the other offer some protection from enemy fire.

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Photos:Aleppo photographer watches city die

Keeping the lights on: The electricity "operations room" in a neighborhood of rebel-held Aleppo.

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Photos:Aleppo photographer watches city die

Two men and their donkey navigate the bombed alleyways of Almarja district in eastern Aleppo.

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Photos:Aleppo photographer watches city die

A mother watches over her children as they return from school; the massive sheet hanging in the street is to deter government snipers.

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Photos:Aleppo photographer watches city die

A street that is monitored by regime snipers.

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Photos:Aleppo photographer watches city die

A stall holder waits for customers; there are reports of some hoarding of rice and flour as the regime's siege tightens.

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Photos:Aleppo photographer watches city die

A street market in Aleppo that is still open despite constant airstrikes -- and the huge slab of concrete hanging over it.

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Photos:Aleppo photographer watches city die

There is still fresh produce in the market stalls but it is more difficult to bring into the city, and much more expensive than even a few weeks ago.

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A UN investigation in late August found that chemical weapons had been used in Syria, both by the national air force and ISIS militants. It found two instances where regime forces had used chlorine as a chemical weapon, and one where ISIS had used mustard gas.

Elsewhere in Aleppo province, ISIS attacked a Turkish military position on Tuesday, killing two soldiers and wounding five others, the Turkish military said in a statement. Another attack killed two Free Syrian Army fighters and injured two others, the military said.

ISIS said its forces destroyed two Turkish tanks with guided missiles in the northern suburbs of Aleppo province, killing a number of Turkish soldiers. It said that a suicide bomber carried out the second attack among FSA soldiers.